The threshold was a log or length of wood placed in the entranceway of the peasant's hut or accommodation provided by the landlord. It contained within the hut the layers of thresh i.e. waste from harvesting corn or wheat. It built up in layers.
The newly wed husband would carry his wife across the thresh hold (threshold) to a comfortable area inside the dwelling - hence they would cross the threshold.
by Philip Hoesli July 7, 2006